The present invention to relates a hoist including a shock absorbing device for the load and to a shock absorbing device for use with a hoist.
Many different designs of hoist are available for mounting in different locations and including different features for different end uses. The present invention is primarily but not exclusively concerned with safety systems by which an operator can enter through a manhole into a tank or pipe for investigation or service. Current regulations require that the operator be attached to a hoist so that in the event any injury or incapacitation, the operator can be returned to the surface by operation of the hoist.
A number of different designs of hoist of this type have been proposed where a base is located on the ground with legs surrounding the entrance hole and a jib portion extending from the base to an upper end where there is provided a cable guide which allows the cable to extend downwardly between the legs into the entrance so that the cable can pass into they underground area through the hole without dragging on the side of the hole. A manually operable winch is conventionally located on the jib portion so that it can be operated to winch the person back to the surface as required.
In view of the foregoing, it is an object of the present invention to provide an improved hoist which includes a single shock absorbing device which operates to provide effective shock absorbing characteristics for two cables.
According to a first aspect of the invention there is provided a hoist comprising:
a base for mounting on a support surface;
a jib portion mounted on the base and extending therefrom to a jib end arranged to be located over a load to be supported;
a first cable pay-out device having a first cable, the first cable pay-out device being mounted on the hoist for paying out and pulling in the first cable;
a second cable pay-out device having a second cable, the second cable pay-out device being mounted on the hoist for paying out and pulling in the second cable;
a first pulley at the jib end for the first cable arranged such that the first cable passes over the first pulley from the first cable pay out device and provides a vertical run of the first cable from the first pulley vertically downwardly to the load which applies a downward force from the load on the first pulley;
a second pulley at the jib end for the second cable arranged such that the second cable passes over the second pulley from the second cable pay out device and provides a vertical run of the first cable from the second pulley vertically downwardly to the load which applies a downward force from the load on the second pulley;
the first cable pay out device being located on the hoist at a first location so that a run of the cable from the first cable pay out device to the first pulley extends at a first angle relative to the vertical run of the first cable;
the second cable pay out device being located on the hoist at a second location different from the first location so that a run of the cable from the second cable pay out device to the second pulley extends at a second angle relative to the vertical run of the second cable which is different from the first angle;
and a shock absorbing device for the pulleys comprising:
a common member arranged for attachment to the jib end with both the first and second pulleys being mounted on the common member at the jib end;
the common member being mounted at the jib end for pivotal movement relative to the jib end about a horizontal axis spaced from the vertical runs of the first and second cables;
the common member including a shock absorbing brake arranged to resist said pivotal movement up to a predetermined load limit such that a downward shock force from the load on at least one of the first and second pulleys causes the common member to pivot downwardly in a shock absorbing action;
the first and second pulleys being arranged such that the distance of the vertical run of the first pulley from the horizontal axis is different from the distance of the vertical run of the second pulley from the horizontal axis.
It is of course an intended or desirable object of the features set forth above that the difference in distance from the axis is related to the difference in the angle so as to tend to equalise the shock force required for and/or the distance moved by the first and second cables. Thus the difference in distance from the axis is generally dependent upon or proportional to a difference in mechanical advantage of the first and second cables generated by the difference in the angle.
The base can be of any construction including but not limited to an element having legs for resting on the surface, a frame for bolted attachment to the surface or a permanently mounted element fastened to the surface.
Preferably the first and second pulleys are mounted with their respective axes of rotation at different distances from the horizontal axis so that the pulleys may be of the same or similar size.
Preferably the common mounting member comprises an arm with the horizontal axis at one end, the first pulley at the other end and the second pulley intermediate the ends and the second pulley is mounted on the arm so as to depend below the arm.
In a preferred arrangement the first pulley is arranged such that the run of the first cable passes over the jib end to the first pulley and the second pulley is arranged such that the run of the second cable passes from below the jib end to the first pulley.
In this preferred arrangement, the first cable pay out device is located on a side of the jib portion away from the jib end and comprises a winch operable to lift the load and wherein the second cable pay out device is located on a side of the jib port facing the jib end and comprises a fall restrain device.
In this preferred arrangement where the second cable extends from below the difference in mechanical advantage is approximately 2:1 so that the difference in distance is also approximately 2:1.
The above term xe2x80x9cshock absorbing brakexe2x80x9d is not intended to limit this invention to any particular form of component which restricts the pivotal movement of the common member. While in a preferred arrangement, this may include clamped brake disks, other restriction devices can be used including frangible couplings and springs.
The use of the term xe2x80x9ccablexe2x80x9d herein is not intended to limit the invention to any particular construction or material and any elongate element suitable for use in lifting or securing a load can be used including rope, chain and the like.
According to a second aspect of the invention is provided the shock absorbing device per se which is defined above and is arranged for use with a hoist of this general type in which two cables are provided at different angles. Thus the present invention includes the aspect of a shock absorbing device sold as a separate element for attachment to an existing hoist. Such an arrangement can include a mounting collar or insert which is designed to engage into or onto an existing jib end and generally but not always this will include a stub shaft which is inserted into an end of the tube forming the jib portion.